Chapter 2

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# Chapter 2 - PowerPoint PPT Presentation

Chapter 2. Scientific Method. Scientific Method. Scientific method- logical approach to solving problems by observing &amp; collecting data, formulating hypotheses, testing hypotheses, formulating theories supported by data Examples of problems… Observable data

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### Chapter 2

Scientific Method

Scientific Method
• Scientific method- logical approach to solving problems by observing & collecting data, formulating hypotheses, testing hypotheses, formulating theories supported by data
• Examples of problems…
• Observable data
• Qualitative = descriptive (turn pink)
• Quantitative = numerical (1 gram)
Data
• We cannot observe everything all at once, so we focus on a system
• System- specific portion of matter chosen for study (ex. Reaction in a test tube)
• Once we obtain data, we can establish patterns
• Patterns can be made into scatter plots, bar graphs, pie charts, etc.
Hypothesis
• Once we have looked for patterns, we form a hypothesis
• Hypothesis- testable statement in the form of “if…then…”
• Then we have to test the hypothesis
• Control(s)- stay constant (placebo)
• Variable(s)- change, only changed one at a time
• If wrong, change or drop hypothesis (might start over)
Hypothesis (con.)
• If correct, explain through models
• Model- explains how events occur or are related in a visual, verbal, or mathematical way
• Theory- broad generalization that explains group of facts or events
• Publish results (letters, scholarly journals, blog, word of mouth)
Metric System
• SI, or SystèmeInternationaled’Unités (French)
• Base units
• Length (lowercase L) = meter (m)
• Mass (m) = kg (kilogram)
• Time (t) = second (s)
• Temperature (T) = Kelvin (K)
• Amount of substance (n) = mole (mol)
• Electric current (I) = ampere (A)
• Luminous intensity (Iv) = candela (cd)
Metric prefixes
• Mega (M) = 10 6
• Kilo (k) = 10 3
• Hecto (h) = 10 2
• Deka (da) = 10 1
• Deci (d) = 10 -1
• Centi (c) = 10 -2
• Milli (m) = 10 -3
• Micro (µ) = 10 -6
• Practice problems on board
Mass vs. Weight
• Mass = amount of matter
• Weight = amount of gravity pull
• On moon, gravity 1/6 that of Earth
• Didn’t lose mass, lost weight
Derived SI units
• Combinations of base units
• Area (A) = lxw = m2 or cm2
• Volume (V) = lxwxh = m3 or cm3
• Density (D) = kg/m3 or g/cm3 or g/mL
• Molar Mass (MM) = kg/mol
• Energy (E) = Joule (J)
Accuracy vs. Precision
• Accuracy- close to accepted value
• Precision- close to measurements made in same way
• Drawings on board
Percent Error
• Goal = 0
• (Experimental – Accepted)/(Accepted) x 100
• Problems on board
Significant figures
• All digits but last one certain
• Rules
• Nonzero = significant
• Zero in between nonzero (2002) = significant
• Zero in front of nonzero = not significant
• Zero at end of number and to right of decimal = significant
• Ex. 2000 = 1 sig, 25.00 = 4 sig, .0001 = 1 sig
• Examples on board
Rounding
• 1->4, round down
• 6->9, round up
• 3.5->4
• 4.5->4
• Sig + or – Sig= same # of decimals
• Sig x or / Sig = same # of sig digits
• Examples on board